Patent GB-1070477-A (GB)
Title: Improvements in and relating to film-stretching apparatus
IPC: B29C55/16
Filed: 1964-08-21
Abstract: 1,070,477. Films. FARBWERKE HOECHST A.G. Aug. 21, 1964 [Aug. 21, 1963], No. 34414/64. Heading B5B. [Also in Division D1] In a tentering apparatus for the simultaneous biaxial stretching of thermoplastic film, the film 3 is held between gripping members 4 while passing from the first film advancing means 1 to the second film advancing means 2, the gripping members gripping the edge portions of the film in the first parallel advancing region being advanced at substantially the   same rate as the film is advanced as it leaves the first film advancing means, and the gripping members gripping the edge portions of the film in the second parallel advancing region being advanced at substantially the same rate as the web is advanced as it approaches the second film advancing means, the gripping members gripping edges of the film in the stretching region being advanced by the film. As shown, film 1 is passed from trio rollers 1, to trio rollers 2 running at a higher speed. In each trio, the axes of the rollers are arranged in an equilateral triangle and the two rollers are driven at the same speed and in the same direction, the third upper roller idling. The clamp system for transverse stretching of the film comprises two groups of clamps 4, each group being freely slideable on an endless profile bar 5. The film is gripped by the clamps 4 in the first parallel advancing region and is then stretched transversely as the clamps move outwardly along the diverging portion of the guide rail 5. The clamps (Fig. 3) consist of a hammer 15 and table 16, the upper lever of the hammer co-operating in known manner with guide rails or plates (not shown) to close and open the clamps at the beginning of the feed zone and the end of the drawing zone respectively. The guide rail 5, supported at 12, 13, is hexagonal in section and engages six roller bearings 14 of the clamps arranged in pairs staggered by 120 degrees. In the first parallel advancing region of the film, the outermost roller firmly contacts V-belt 11 running over driven V-belt pulleys 6 thus shifting the clamps along the profile bars 5. In the stretching zone the clamps have no contact with the belt and are moved along the guide rails by the motion of the film. In the second parallel advancing region of the film the outermost roller of each clamp contacts V-belt 10, driven from pulley 7 and supported by pressure rollers 9 (Fig. 3), again shifting the clamps along the guide rail 5. Guide pulleys 8 for V-belt 10 may be swung away from profile bar 5 in the direction of the arrow, so as to extend or reduce section 5 of the profile bar to adjust it to the number of clamps to be stored, which number varies with the longitudinal drawing ratio. The whole frame may be swung in an infinitely variable manner about a horizontal axis transverse to the direction of movement of the web, so as to alter the weight component of the clamps acting on the web in the drawing zone, according to the material being processed. The endless profile bars 5 are desirably disposed so that they can be brought closer together or moved apart from one another so as to obtain different drawing ratios and adjust the apparatus for film of different widths.